Captain Shortwave

Cold air still on target and the Azores low is fragmenting with a weather front pushing north into southern England. Where these two meet could result in a lot of snow. Worth noting that the surface high is not present on this run.

The GFS has more cold air digging south upstream and the Azores low (which this feeds) is being allowed to move which means the Iberian ridge should flatten quicker on this run. The cold air may take a little longer to arrive but unsure whether this will be better or worse than the previous run.

Well there were a few snow grains when I left work in Huntingdon, so technically I have seen something.

The clear skies over the continent will be in association with drier air that will bring clear skies over the next couple of days. This will clear the stratified clouds that most have seen today. This will likely kill off convection (less moisture, less showers) but there may still be some scattered showers before the cold air fully clear.

The only chance of seeing a flake here is probably on the confectionery section of the local supermarket….. Best of luck for those getting snow today.

A much much better first plunge of cold air, arriving across the south around early afternoon on the 15th.

Mostly cloudy here with just the odd hole in the cloud. Not expecting anything up here, though some models do suggest the chance of a brief stream of light showers moving in from the Wash this evening.

The ECM appears to be going a similar route to the previous run, the only difference being the strong warm air advection going into the Arctic. Where will the developing arctic high end up, if it can drift over the top of the troughing to our east and push things far enough south then things could look interesting by the end of the run. Cold air arrive in the day6/7 range looks like a good bet now, however the model output does have one big element of concern and this is the secondary push of cold air from the Atlantic and the models are flirting with spilling this south west into the Atlantic instead of pulling this cleanly southwards.

Like the GFS, we do get some arctic air down across the UK at day7/8 but with high pressure more in charge so it’s mostly dry, hence the second attempt to bring the more unstable northerly. A much better run from the ECM and the models suite is a lot better than the 00z for instance.

Already earlier on you can see the subtle shifts northwards compared to yesterday. Also the cold pool tomorrow is now covering the Midlands southwards, pretty much in line with the rest.

Hmm any upgrades regarding that cold pool will have impacts as it passes to the west of the UK and comes up against the Ridging in the Atlantic, in particular that impacts the timeline of when the southern arm of the jet gets cut off. The longer this takes, the further north the high could sit in the mid range. Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4999558

This post assumes that the first plunge of cold air won’t arrive (around the 15th, which is day 8). Given that even the GFS gets cold air over the UK (even if heights are too high for anything of note snow wise) and the others look much better, then this seems like a rather bold statement. Secondly it is important to note that the angle of the ridge is much better and as such would deliver cold for on the GFS later on, in comparison to the 06z where the ridge was negatively tilted to the extent where the heights were pulled clean away from the Atlantic.

The GFS whilst not as good with the initial plunge, it does deliver a much better wedge opportunity. The high should cut off close to Greenland instead of being blown away.

Ironically the GEM is too good and we end up under generally slack low heights. The temperatures are pretty brutal with widespread ice days once the cold air arrives. This run would be -20c minima territory in the north, would need things to crop up to generate snow though.

The models have toyed with a strong Pacific ridge, a flatter solution and now the main models have something in between, a parcel of heights moving across towards Greenland. Now that would be a big stroke of luck because suddenly we just need the Atlantic ridge to push north enough to meet what is coming from the other side. When they meet we will have the amplified ridge that we saw made solely from our side a couple of days ago.

Hmm any upgrades regarding that cold pool will have impacts as it passes to the west of the UK and comes up against the Ridging in the Atlantic, in particular that impacts the timeline of when the southern arm of the jet gets cut off. The longer this takes, the further north the high could sit in the mid range.

Again no point worrying about an ECM run that has deviated so much from its previous run. In a way it is sort of entertaining to see how it manages to scupper cold weather for the UK on each run. This time because the Azores low gets trapped, it is allowed to pump warm air into SW Europe instead of the low engaging the cold air and moving in a general easterly direction.

The ECM has managed to create the situation where the Azores low is filling in situ, not a single other model output has done this, even the ECM op on previous runs.

Well it is further north east at a 12 hour earlier timeframe, so it is better, given it is on the move it might be worth watching as to whether this acts as the trigger low in a few frames time.

A certain someone is going to be late if the ICON is correct For the record this is probably the best run so far this year, purely because of how quick and clean the retrograde is.

Secondary low forming in very cold air north of Scotland that should head southwards and yes the Atlantic ridge is reamplifying. As I said a couple of days ago, an Atlantic ridge is fine to sustain cold if we can keep the pattern upstream conductive to reinvigorate the pattern, the northerly on the GFS is as potent as I have seen in many years.

We need that deep low exiting Canada to fully interact with the cut of low to push the ridge northwards again, a cold northerly is guaranteed but upstream is the difference between a toppler and something more significant. -8c isotherm south of the UK by day 9.

ICON shows mostly light snow pushing south west through the Thames Estuary during Monday, this becomes more widespread during Monday night as the winds veer more easterly and the atmosphere is a little more unstable, and it is this period where a dusting could anywhere south of the Wash (Very little will settle during the day unless the precipitation is heavier). Apart from getting agreement on the depth of cold that could push into the south on Monday, there isn’t much point looking too much into precipitation, as many can add to this, snow can crop up unexpectedly (For instance in Great Yarmouth in January 2013 we saw a couple of inches of snow that came from a single shower that formed in the southern North Sea that was dragged onshore by the approaching Atlantic trough that was never picked up by the models and as such the weather warning was issued during the event itself). So let’s see what happens and of course next weekend onwards also poses a lot of interest.

ECM day 6 The ECM is much slower at shifting the residual low heights around Greenland at this point. That low trundles around only ending up east of the UK at day 10. Meanwhile the other models have that low well on its way in its travels around the UK high.

A completely different orientation of the Pacific ridge in this run, pushing right through Alaska and interacting with the Atlantic ridge. Previous runs did not have this keeping the discreet Atlantic ridge and trying to build the block from this alone. The cold will come and the polar profile is quite astonishing here. Todays 12z vs yesterday’s